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INTRODUCTION: Tweety homolog1 (Ttyh1) is a presumed volume-regulated Cl-channel. It has been proposed to participate in the regulation of neuronal morphology. AIM(S): We aimed to examine dendritic arborization and spine morphology of pyramidal neurons following TTYH1 overexpression in organotypic hippocampal cultures. METHOD(S): Rat organotypic cultures were co-transfected with TTYH1‑GFP‑Synapsin and RFP‑β‑actin constructs, using biolistic transfection (Gene-Gun, BioRad). Neuronal reconstructions of CA1 and CA3 pyramidal cells were obtained with confocal microscopy and Neuromantic software. Morphometric assessments of individual neurons were performed with Sholl method. L-measure software was used to extract more complex quantitative measurements from neuronal reconstructions. Changes in spine morphology and density on CA1 and CA3 neurons were studied with SpineMagick software. RESULTS: Sholl method did not reveal signifficant differences in dendritic arborization of neurons overexpressing TTYH1 compared to control neurons. L-measure revealed that CA3 neurons overexpressing TTYH1 showed increased average branch length in the seventh branch order of apical dendrites (P<0.05) and increased number of branches in the third branch order of basal dendrites (P<0.01). CA1 pyramidal neurons overexpressing TTYH1 showed reduced average branch length in the third (P<0.05) and fourth (P<0.001) branch orders of basal dendrites. TTYH1 overexpression led to increased number of stubby spines on CA1 neurons (apical proximal and distal dendrites: P<0.01; basal dendrites: P<0.05) and CA3 neurons (apical proximal dendrites: P<0.01). Decrease in the number of long spines on CA1 neurons (apical proximal and distal dendrites: P<0.01) and CA3 neurons was confirmed (apical proximal dendrites: P<0.05). CONCLUSIONS: The influence of TTYH1 overexpression on dendritic complexity and spines morphology suggests that TTYH1 protein may be involved in neuronal plasticity. FINANCIAL SUPPORT: This research was supported by Polish National Science Centre Grant 2011/03/B/ NZ4/00302.